Relatively little is known about alcohol's effects in adolescence, a critical stage of human development. This is true despite the facts that: 1) the majority of individuals began experimenting with alcohol as teenagers, 2) drinking beginning in adolescence is one of the most powerful predictors of later alcohol abuse, and 3) in adolescence, there are changes in the areas of the brain that modulate drug reinforcement. In addition, most studies of the impact of alcohol dependence on the brain have examined individuals in treatment. Such samples represent a small proportion of alcoholics in the general population, and we have shown that treated adult alcoholics are not a representative sample of the general population of adult alcoholics with more intense early trajectory of alcohol consumption and with greater comorbid psychopathology and abnormal psychological functioning. Until proven otherwise, a reasonable assumption is that adolescents in treatment for alcohol use disorders (AUDs) are also heavier drinkers with more comorbidities than untreated adolescents with AUDs in the general population. For this reason, it is crucially important to study adolescent alcohol abusers in the community in order to understand the effects of alcohol abuse on the adolescent brain in the population at large. Moreover, it is important to study community adolescents with AUDs, but without other substance use disorders (SUDs). To do otherwise, would make it impossible to disentangle the effects of AUDs from those of other SUDs on brain structure and function. This goal has not been achievable in the United States, because the vast majority of adolescents with AUDs also have other SUDs. In the Cape Town region of South Africa, a unique opportunity to study 'pure'adolescent AUDs exists (we have documented this in a pilot study). We propose to recruit and study 100 such adolescents with AUDs (12 - 18 years of age, half males and half females), and 100 light/non-drinker age and gender matched controls, all without other SUDs or current diagnosable comorbid psychopathology. Subjects will be studied in four domains: psychological functioning, neuropsychological functioning, brain structure, and electrophysiological measures of brain function. We will be uniquely able to isolate the effects of AUDs on brain structure and function in adolescence.